Two important areas of medicine are cancer chemotherapy and chemical modifications of the immune system. These have been the focus of much recent medical research.
A major problem affecting the efficacy of chemotherapy regimens is the evolution of cells which, upon exposure to a chemotherapeutic drug, become resistant to a multitude of structurally unrelated drugs and therapeutic agents. The appearance of such multi-drug resistance often occurs in the presence of overexpression of the 170-kDA membrane P-glycoprotein (gp-170). The gp-170 protein is present in the plasma membranes of some healthy tissues, in addition to cancer cell lines, and is homologous to bacterial transport proteins (Hait et al., Cancer Communications, Vol. 1(1), 35 (1989); West, TIBS, Vol. 15, 42 (1990)). The protein acts as an export pump, conferring drug resistance through active extrusion of toxic chemicals. Although the mechanism for the pump is unknown, it is speculated that the gp-170 protein functions by expelling substances that share certain chemical or physical characteristics, such as hydrophobicity, the presence of carbonyl groups, or the existence of a glutathione conjugate (see West).
Various chemical agents have been administered to repress multi-drug resistance and restore drug sensitivity. While some drugs have improved the responsiveness of multi-drug resistant ("MDR") cells to chemotherapeutic agents, they have often been accompanied by undesirable clinical side effects (see Hait et al.). For example, although cyclosporin A ("CsA"), a widely accepted immunosuppressant, can sensitize certain carcinoma cells to chemotherapeutic agents (Slater et al., Br. J. Cancer, Vol. 54, 235 (1986)), the concentrations needed to achieve that effect produce significant immunosuppression in patients whose immune systems are already compromised by chemotherapy (see Hait et al.). In addition, CsA usage is often accompanied by adverse side effects including nephrotoxicity, hepatotoxicity and central nervous system disorders. Similarly, calcium transport blockers and calmodulin inhibitors both sensitize MDR cells, but each produces undesirable physiological effects (see Hait et al.; Twentyman et al., Br. J. Cancer, Vol. 56, 55 (1987)).
Recent developments have led to agents said to be of potentially greater clinical value in the sensitization of MDR cells. These agents include analogs of CsA which do not exert an immunosuppressive effect, such as 11-methyl-leucine cyclosporin (11-met-leu CsA) (see Hait et al.; Twentyman et al.), or agents that may be effective at low doses, such as the immunosuppressant FK-506 (Epand and Epand, Anti-Cancer Drug Design 6, 189 (1991)). Despite these developments, the need remains for effective agents which may be used to resensitize MDR cells to therapeutic or prophylactic agents or to prevent the development of multi-drug resistance.
A second significant medical objective constitutes the ability to modulate the immune system. For example, post operative graft rejections are a major complication affecting the success of bone marrow and organ transplantations. However, through the use of immunosuppressive drug therapy, graft rejection in organ transplantation can be significantly reduced. Immunosuppressive therapy may also be used in preventing or treating autoimmune diseases, which are similar to graft rejection, except that the rejection is of self tissue.
One widely accepted immunosuppressant for the prevention of graft rejection is CsA. A natural product of fungal metabolism, CsA has been demonstrated to have potent immunosuppressive activity in clinical organ transplantations. Calne, R. Y. et al., Br. Med. J., Vol. 282, pp. 934-936 (1981); White, D. J. C., Drugs, Vol. 24, pp. 322-334 (1982).
Many disorders have been treated with cyclosporin A with positive results, confirming the importance of the autoimmune component in these diseases and their effective treatment with compounds working by selective T-cell immune suppression similar to cyclosporin A. These disorders include ophthalmological diseases, such as uveitis, Nussenblatt, R. B. et al., Lancet, pp. 235-238 (1983); Behcet's disease,* French-Constant, C. et al., Lancet, p. 454 (1983); Sanders, M. et al., Lancet, pp. 454-455 (1983); and Grave's ophthalmopathy, Weetman, A. P. et al., Lancet, pp. 486-489 (1982). FNT Cyclosporin A is currently approved in Japan for the treatment of Behcet's disease, the first autoimmune disease indication for this compound.
CsA has also been used in dermatological applications, including various autoimmune skin diseases, such as psoriasis, Ellis, C. N. et al., J. Amer. Med. Assoc., Vol. 256, pp. 3110-3116 (1986); Griffiths, C. E. M. et al., Brit. Med. J., Vol. 293, pp. 731-732 (1986); acute dermatomyositis, Zabel, P. et al., Lancet, p. 343 (1984); atopic skin disease, van Joost, T. et al., Arch. Dermatol., Vol. 123, pp. 166-167 (1987); scleroderma, Appleboom, T. et al., Amer. J. Med, Vol. 82, pp. 866-867 (1987); and eczema, Logan, R. A. and Camo R. D. R., J. Roy. Soc. Med., Vol. 81, pp. 417-418 (1988).
Various hematological diseases treated with CsA include anemia, such as aplastic anemia, Stryckmans, P. A. et al., New Engl. J. Med., Vol. 310, pp. 655-656 (1984); and Gluckman, E. et al., Bone Marrow Transplant, Vol. 3 Suppl. 1, 241 (1988); and pure red cell aplasia (PRCA), Toetterman, T. H. et al., Lancet, p. 693 (1984).
CsA has also been used in the fields of gastroenterology and hepatology to treat primary cirrhosis, Wiesner, R. H. et al., Hepatology, Vol. 7, p. 1025, Abst. #9 (1987); autoimmune hepatitis, Hyams, J. S. et al., Gastroenterology, Vol. 93, pp. 890-893 (1987); ulcerative colitis, Porro, G. B. et al., Ital. J. Gastroenterol., Vol. 19, pp. 40-41 (1987); Crohn's disease, Allison, M. C. et al., Lancet, pp. 902-903 (1984), and Brynskov, J. et al., Gastroenterology, Vol. 92, p. 1330 (1987); and other gastrointestinal autoimmune diseases.
Neurological applications of CsA include amyotrophic lateral sclerosis (ALS, "Lou Gehrig's disease"), Appel, S. H. et al., Arch. Neurol., Vol. 45, pp. 381-386 (1988); myasthenia gravis, Tindall, R. S. A. et al., New Engl. J. Med., Vol. 316, pp. 719-724 (1987); and multiple sclerosis, Ann. Neurol., Vol. 24, No. 1, p. 169,m Abstract P174 (1988), and Dommasch, D. et al., Neurology, Vol. 38 Suppl. 2, pp. 28-29 (1988).
CsA has been used to treat nephrotic syndromes, membrano-proliferative glomerulonephritis (MPGN) and related diseases, Watzon, A. R. et al., Clin. Nephrol., Vol. 25, pp. 273-274 (1986); Tejani, A. et al., Kidney Int., Vol. 33, pp. 729-734 (1988); Meyrier, A. et al., Transplat Proc., Vol. 20, Suppl. 4 (Book III), pp. 259-261 (1988); LaGrue, G. et al., Nephron., Vol. 44, pp. 382-382 (1986).
In addition, CsA has been used to treat rheumatoid arthritis, Harper, J. I. et al., Lancet, pp. 981-982 (1984); Van Rijthoven, A. W. et al., Ann. Rheum. Dis., Vol. 45, pp. 726-731 (1986), and Dougados, M. et al., Ann Rheum. Dis., Vol. 47, pp. 127-133 (1988); and insulin-dependent diabetes mellitus (IDDM), Stiller, C. R. et al., Science, Vol. 233, pp. 1362-1367 (1984), Assan, R. et al., Lancet, pp. 67-71 (1985); Bougneres, P. F. et al., New Engl. J. Med., Vol. 318, pp. 663-670 (1988), and Diabetes, Vol. 37, pp. 1574-1582 (1988).
Many veterinary diseases are also characterized as autoimmune diseases. Autoimmune diseases such as those discussed above have been observed in mammals. Papa, F. O. et al., Equine Vet. J., Vol. 22, pp. 145-146 (1990)--infertility of autoimmune origin in the stallion; Gorman, N. T. and L. L. Werner, Brit. Vet. J., Vol. 142, pp. 403-410, 491-497 and 498-505 (1986)--immune mediated diseases of cats and dogs; George, L. W. and S. L White, Vet. Clin. North Amer., Vol. 6, pp. 209-213 (1984)--autoimmune skin diseases in large mammals; Bennett, D., In. Pract., Vol. 6, pp. 74-86 (1984)--autoimmune diseases in dogs; Halliwell, R. E., J. Amer. Vet. Assoc., Vol. 181, pp. 1088-1096 (1982)--autoimmune diseases in domesticated animals.
The mechanism by which CsA causes immunosuppression has been established. In vitro, CsA inhibits the release of lymphokines, such as interleukin 2 (IL-2) [Bunjes, D. et al., Eur. J. Immunol., Vol. 11, pp. 657-661 (1981)] and prevents clonal expansion of helper and cytotoxic T cells [Larsson, E., J. Immunol., Vol. 124, pp. 2828-2833 (1980)]. CsA has been shown to bind the cytosolic protein, cyclophilin, and inhibit the prolyl-peptidyl cis-trans isomerase (PPIase) activity of that protein. Fischer, G. et al., Nature, Vol. 337, pp. 476-478 (1989); Takashaski, N. et al., Nature, Vol. 337, pp. 473-475 (1989).
Recently, a second natural product isolated from Streptomyces, referred to as FK-506, has been demonstrated to be a potent immunosuppressive agent. Tanaka, H. et al., J. Am. Chem. Soc., Vol. 109, pp. 5031-5033 (1987). FK-506 inhibits IL-2 production, inhibits mixed lymphocyte culture response and inhibits cytotoxic T-cell generation in vitro at 100 times lower concentration than cyclosporin A. Kino, T. et al., J. Antibiot., Vol. 15, pp. 1256-1265 (1987). FK-506 also inhibits PPIase activity, but is structurally different from CsA and binds to a binding protein (FKBP) distinct from cyclophilin. Harding, M. W. et al., Nature, Vol. 341, pp. 758-760 (1989); Siekierka, J. J., Nature, Vol. 341, pp. 755-757 (1989).
In view of the wide variety of disorders that may be alleviated by immunosuppression, and the scant number of available immunosuppressants, there remains a great need for novel immunosuppressive agents. Such agents may be used alone or serve as supplemental therapeutics to CsA and FK-506.